1. Field of the Invention
This invention relates generally to ball valves for use particularly in conduit manifold systems and more particularly concerns a compact manifold ball valve having fire-safe features to maintain the sealing integrity thereof when the valve has been subjected to sufficient heat for a sufficient period of time to destroy the elastomer and polymer sealing elements thereof. More particularly, the present invention is directed to a ball valve mechanism having a ball defining integral trunnions which are supported for rotation within the valve chamber by trunnion support and bearing assemblies which are free to shift and permit the valve ball element to be self-centering with respect to either of two seat assemblies that are disposed within seat pockets that are also defined by the valve body. Additionally, the present invention concerns a compact trunnion type ball valve having an actuating stem and a seat retainer which are blow-out proof even under conditions of fire.
2. Description Of The Prior Art
Compact manifold ball valves currently manufactured and used in manifold testing systems utilize floating balls and when in the closed position, produce excessive loads on the downstream seats, therefore creating high operating torques that are undesirable. These increased torques also cause excessive wear on the downstream seal and eventually destroy the same. In addition, gear operators or other types of actuators with high output torques are commonly required to operate this type of manifold valve, resulting in additional costs. It is desirable therefore to provide a ball valve mechanism which incorporates a mechanism for preventing downstream movement of the flow controlling ball element responsive to pressure and therefore eliminating excessive force of the valve ball against the downstream seat.
Another problem that is frequently present in test manifolds having ball valves for flow control is the fire hazard that is virtually always present. In the event of excessive heat from a fire, the elastomer seals and polymer seats of typical floating ball valves will likely be destroyed and the fluid within the flow lines will leak past the void seat pockets and may leak past the stem. This leakage can be sufficient to feed the fire when the valve is used for controlling a combustible fluid medium such as petroleum products. It is desirable therefore to provide a ball valve mechanism for use in flow controlling manifolds which incorporates a high temperature sealing capability to ensure product leakage to downstream of the valve mechanism or to atmosphere is controlled within a range of zero to minimum leakage rates as permitted by various industry fire test standards such as API Specification 6FA or other similar specifications in the event a condition of excessive heat is encountered.
The trunnion support elements have axial clearances with respect to the valve ball structure and with the valve body structure as shown in FIGS. 1, 2 and 5-9, which permit the valve ball, even though it is trunnion supported, to shift axially perpendicularly or horizontally and thus ensure precise centering of the valve ball and valve seats with respect to one another. This feature promotes efficient sealing engagement between the valve seats and valve ball when the valve is assembled and also enhance the metal-to-metal sealing capability of the valve mechanism in the event the seals of the valve should become damaged by excessive heat.
The xe2x80x9ccompactxe2x80x9d nature of the ball valve mechanism of the present invention generally results from a short or compact valve body having opposed xe2x80x9copenxe2x80x9d ends each defining a flange closure seat which is engaged by and establishes sealing with a flange closure which may be defined by a flange of a pipe section of the manifold or other piping assembly. Since no other body closure members are provided, the overall length of the valve body is short and compact as compared with the valve body structures of the conventional ball valves. Thus, the compact manifold ball valves of the present invention is capable of being installed in piping systems such as the flow control manifolds of offshore production platforms where minimal space is available for valve installation. The compact trunnion type manifold ball valve described in this specification has a ball with integral opposing trunnions that rotate in trunnion bearing supports. The trunnion bearing supports contain a cylindrical sleeve type bearing to reduce friction during rotation of the ball from closed to open position or vice versa. The trunnion bearing supports are prevented from moving axially by one end abutting a precision machined shoulder in the valve body and the opposite end abutting the inner face of a threaded seat retainer. The trunnion bearing supports are free to shift in positions of axially, perpendicularly or horizontally sufficient to permit the ball to center into either seat assembly that is being pressure energized for positive sealing of the seat assembly insert to the ball spherical surface. This design eliminates the need for alignment pins or other means for the positioning of similar types of trunnion bearing supports offered in competitive ball valves. The load created by differential pressure when the ball is in a closed position is transmitted against the trunnion bearing rather than the downstream seat as in conventional floating ball valve designs, resulting in lower operating torque. The upstream seat load on the valve is very minimal in comparison to the load on the downstream seats in the floating ball valve designs. Actually, the reduction in seat load by using the trunnion type ball valve may be in the range of from about 60% to about 80% less, therefore minimizing wear and accomplishing longer service life of the valve seats as well as providing for lower maintenance costs as compared to floating ball valves. In addition, gear operators or actuators are not normally required to operate the compact trunnion type manifold ball valve until larger sizes and higher pressure classes of valves are used in service.